THE ANATOMY OF WOODY PLANTS 



microsporophyll is, however, of greater interest in the present 

 connection. In the petiole of the bisporangiate microsporophyll 

 tracheary elements of a centripetal character occur on the upper 

 side of the protoxylem (Fig. 224). These elements can scarcely 

 be said to constitute typical centripetal 

 tracheids, since they are often of wide 

 lumen and are correspondingly abbrevi- 

 ated in length. As the foliar traces 

 ascend into proximity to the sporangia, 

 they separate from one another and the 

 xylem of each rotates so as to occupy a 

 position near the middle line of the 



a b 



FIG. 224. (a) longitudinal, (b) transverse, section of wood of bundle in micro- 

 sporophyll of Ginkgo. 



sporophyll, while the strands of phloem turn outward, to end in the 

 bases of the sporangia. Meanwhile the transfusion elements occur- 

 ring on the upper side of the tracheary strands in their upward 

 course pass imperceptibly into the fibrously thickened mechanical 

 elements which are responsible for the dehiscence of the sporangium. 

 Further, the apex of the tracheary strands passes gradually by 

 means of short transfusion tracheids into the mechanical elements 

 which lie along the median sides of the sporangia. In this fashion 

 there is established an intimate relation between the tracheary 

 tissues of the bundles of the reticulate cells which constitute the 



